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Foe finder Life as a worker ant is a constant struggle, gathering food and protecting the nest, but having damaged antennae could make survival even harder, according to a new Australian study.

Professor Mark Elgar, an evolutionary biologist at the University of Melbourne, and colleagues, have found that ants with damaged antennae aren't able to determine friend from foe as easily as those with pristine antennae.

"We have shown if the hairs on the antennae have been damaged by battles or normal wear and tear, then the ant's ability to detect the right message and respond appropriately is compromised," says Elgar.

Elgar and colleagues looked at the behaviour of the green tree ant (Oecophylla smaragdina), which is found throughout northern Australia and southern parts of Asia.

"They are very visual, when you see them on the nests they've got beautiful long legs … very very elegant," says Elgar. "We also know that they are very aggressive."

"If you ever come across one of their nests, which are built out of leaves, there will be large numbers of ants guarding it. If you move your finger from side to side you will see the ants follow. But like most ants they live in a chemical world."

Ants rely on information gathered by their antennae to find food, mates and safe places for their offspring. They also use them to detect whether other ants are from their nest or a rival's.

"The antenna is a critical part of receiving this kind of information. They have receptors elsewhere on their body, but there's a huge concentration on their antennae," says Elgar.

The researchers examined the sensilla (hairs) on the ants' antennae and compared this to their ability to sniff out the enemy. They found that ants with fewer sensilla reacted less aggressively to non-nest mate enemies.

"The pattern is so strong that even using this crude measure, we're actually able to discern this negative correlation," says Elgar. "If we had used electron microscopy I'm pretty sure the correlation would be much tighter."

Receiver's perspective

He suggests damaged antennae on ants may be due to wear and tear or combat in the field, not ageing.

"Ants don't age the way we do - the moment they're slightly decrepit they're pretty much dead. The opportunity for age-related decay that we see in humans is a lot less in a worker ant."

Elgar says one of the reasons for undertaking the study was to look at animal communication from the receiver's perspective.

"There's lots of information that looks at the signal, such as the colours of birds and how they use them to attract females. But almost nothing has been done on how good receivers are receiving that signal," he says